1. Field of the Invention
The present invention relates to an improvement of a waterproof type electronic apparatus unit which is suitable for an on-vehicle electronic control apparatus installed in an engine compartment, for example.
2. Description of the Related Art
There is a waterproof type electronic apparatus unit configured to house a circuit board, on which a plurality of circuit components and a connector housing (tall component) are mounted, in a sealed case body, allowing a part of the connector housing to be exposed from the case body so as to connect with a mating connector. The case body that houses this electronic apparatus unit is constituted by a case having a space to house the circuit board and a flat cover which covers the case, where the case and the flat cover are secured by screws, or is constituted by a flat base, on which the circuit board is mounted, and a deep cover which covers the base. Mounting legs are installed on either the case or the base and fixed to the mounted surface by set screws. A waterproof seal material is applied to the surfaces joining the base (or the case), the cover and the connector housing, and a water repellent filter is disposed on the inner surface of the base (or the case). This water repellent filter is configured to prevent the entry of water drops into the case body, and is constituted by a flat porous material including a plurality of micro-pores which allow the free passage of air, so that the air inside the case body is open to the outside air, in order to prevent the deformation of the case body structure or damage to the air tight seal structure, which is caused by the atmospheric pressure difference between the inside and the outside of the case body, due to an increase in the temperature of the components that heat up inside the case body.
For example, according to FIG. 1, FIG. 3 and FIG. 7 of the “board housing case body of on-vehicle electronic apparatus” disclosed in Japanese Patent Application Laid-open No. 2013-004611, the circuit board 40, on which the connector housing 41 is mounted, is sealed hermetically inside the board housing case body 10 constituted by a base 30 (made of sheet metal) and a cover 20 (made of sheet metal), the mounting legs 31 and 32 are disposed on the base 30 and are fixed to the mounted source (not illustrated), and the cover 20 is integrated with the base 30 by bending the bending pieces 25a to 25d disposed at four corners of the cover 20. It is stated that four screws may be used instead of the bending pieces 25a to 25d (see paragraph [0050]), but the circuit board 40 is held at three sides between the base 30 and the cover 20. In Japanese Patent Application Laid-open No. 2013-004611, it is disclosed that the connector housing 41 is disposed between the circuit board 40 and the cover 20, and an aluminum die cast cover may be used instead of the sheet metal cover (see paragraph [0049]).
According to FIG. 2 and FIG. 3 of the “electronic circuit unit” disclosed in Japanese Patent Application Laid-open No. 2007-073764, the circuit board is constituted by a waterproof case 2 which houses the circuit board in a waterproofed state, a base member 6 (made of metal) which front surface supports the rear surface of the circuit board, and a cover member 7 (made of resin) which covers the front surface of the circuit board and is fixed to the base member 6, and a rear surface 6f of the base member 6 is exposed so that the heat generated from the electronic components 4 on the circuit board 3 transfers through the base member 6 and is discharged from the rear surface 6f, thereby the heat in the circuit board in the waterproofed state can be dissipated satisfactorily. The cover member 7 is outsert-molded and fixed to the circuit board 3 and the base member 6, which are in a mutually fixed state, and the resin constituting the cover member 7 is thermoplastic polymeric resin, which is suitable for outsert-molding (see paragraph [0017]).